Devices communicating by means of wireless technology run the risk of encountering interference in environments where other wireless technologies are in use. One of the possibilities to overcome this issue is to switch to an undisturbed communication channel, for example by switching the frequency used. Such frequency hopping systems face the challenge to re-synchronize a transmitting and a receiving device.
In frequency hopping, a signal is transmitted on a bandwidth considerably larger than the frequency content of the original information. There exist so-called spread spectrum techniques which employ pseudo-random numbers to determine and control the spreading pattern of the signal across the allowed bandwidth. Examples of these spread spectrum techniques are frequency hopping spread spectrum, FHSS, which is used e.g. by Bluetooth, direct sequence spread spectrum, DSSS, which is used e.g. by Zigbee, and time hopping spread spectrum, THSS, which is used in second-generation mobile cellular networks. Also combinations of these techniques are possible.
All of these techniques use a different strategy to achieve resynchronization of transmitting and receiving device after switching the communication channel. For instance, the approach in Bluetooth is that the transmitting device uses all the channels in a fixed period of time. The communication channel is changed for every time slot. The receiving device retrieves the channel of the transmitting device by picking a random channel, staying in that channel, and listening for valid data. This takes time and increases current consumption in the devices involved.